I have a 2003 Cargo Van with a 318 and has 120,000 miles on it. I was losing oil pressure when I would accelerate rapidly at high RPMs. The pressure gage would instantly drop to 0 and the valves would soon start tapping. But if I pulled over and shut the engine off the pressure would come back up to normal, aprox 60 psi. and be ok until I would have accelerate rapidly again. But now I lost oil pressure and it won't come back up. I had the oil pump changed with a high vilosity pump and anew filter and oil, and still have no oil pressure, and the valves are tapping so I know its not just the sending unit. The lower end sounds good, no noise.The mechanic that changed the pump said he thought it may have bad cam bearings, but would this cause instant oil pressurelossat highrpm and now no pressure? The pressure was allways either good or 0 never low.Is there a pressure relief valve outside ofthe oil pump?I must be overlooking somethingfor the pressure to come up to normalafter shutting the engine off and restarting. I would very much appreciate any advice before I have to replace the engine, Thanks, Dan

 

The one and onlycheck valve is built into the pump. It's not a cam, rod, or mainbearing problem.

I can think of two possibilities that would cause this.

1. The corners of the hex shaft that drives the pump are rounded off, causing slippage under heavy load. But this should've been obvious to whomever changed the pump.

2. There is a chunk of sludge or other debris in your oil passage leading to the top of the motor. I say the top because you said the bottom stays quiet. At low RPMs the debris just sits there and allows oil to pass. However, when you rapidly accelerate the oil flow picks up dramatically and pulls the debris along until it hits a narrower part of the oil passage. When this happens oil flow is cut off to the top of the motorand your pressure gauge also drops since it reads the pressure up there. Once you turn the motor off, the oil flow stops and the debris is allowed to settle until the next high RPM situation. The problem you have now is that chunk of debris isn't falling and is lodged tight, effectively prevent the oil from flowing even when you first start it up.

You could try motor flush because there could be some oil passing the blockage, just not enough to build pressure. The other alternative is to tear the motor down and have the block dipped to clean it up like new.

 

I'll bet your right alloro. I had the heads replaced at 100,00 miles and I'll bet that a piece of gasket material or something got into the oil gallery and was working like a valve and is now stuck. Im going to pull the pan, pump, valve covers, and try to clean the gallerys. Can I access the gallerys from where thepump bolts up?I'll try to clean the gallerys from the pump inletwith flexablesteel cable casing, then maybe blow out with compressed air through flex plastic tubing.Or is there a better way to go about it? Thank you alloro i appreciate it very much and will post the the results. Thanks, Dan

 

Compressed air might work, but since there is oil in the passages, a piece of gasket material can stick to the sidepretty good. The compressed air might clear the blockage but not push the debris out the other end. This leaves the potential for it to happen again sometime. If you're going to do it the way you described, I'd first run motor flush through the engine to help thin the oil and make it less sticky.

The first place to check for any blockage is between the sending unit and the filter. Remove them both and blow air into the sending unit hole. Maybe you'll get lucky enough to not have to go any further.

Accessing all of the oil passages without pulling the motor is not possible. There are a few 3/8" female square head screwed in plugs around the motor that block off the ends of the oil passages. Two of them are on the back of the motor and are only accessible if the motor and tranny are separated.

When the pump was changed, did anyone check the pickup tube to make sure it was clean inside?

 

Thanks Again alloro, I will try to clear the oil passage between the sender and the filter first.
Do i have todissconnect both motor mounts to get the pan off? and fanshroud?

 

No motor mounts need to be disconnected, nor the fan shroud.

Remove or disconnect the following:
Oil filter
Starter motor
Cooler lines
Oil level sensor connector
Heated Oxygen (HO2) sensor connector
Exhaust Y-pipe
Oil pan

 

Looks like I will have to dissconnect the motor mounts, The pan is dissconnected and tight on top of the suspension cross member, the pan looks like it has to drop down at least 2 or 3 inches to miss the flywheel. Any sugestion will be appreciated Thanks, Dan

 

Also it looks like a new oil pump was not installed, The only bolts that show signs of being removed where the pan bolts, I belive the mechanic gave up and told me he put a high vilocity pump in. Then said the motor was shot\ bad cam bearings. Cant wait to get the pan off!

 

Also I used 60 psi air pressure to blow out the passage between the sending unit and filter, No blockage. I started the engine with the filter off and the pan full of oil and no oil pumped from the filter connection, Is this connected directly to the pump? Thanks Again, Dan

 

Oil should've blow out of the oil filter base like crazy. Your pump isn't working or your pickup tube is clogged.